The present invention relates to absorbent articles.
A various assortment of absorbent articles, such as disposable diapers, have been proposed for use in capturing and retaining body fluids when placed against a wearer. For example, disposable diapers are normally made with a fluid pervious cover sheet, a fluid impervious backing sheet, and an absorbent pad positioned between the cover and backing sheets. Many of such pads are made from wood fluff which is normally formed by fiberizing or comminuting pulp board. The pump board itself is normally formed from trees through a pulping process. The pulping processes may be categorized as chemical, semichemical, mechanical, and thermomechanical.
All of the wood fluff used in absorbent articles sold in the United States known to the applicant has been predominantly formed from a chemically produced pulp. For a given species of wood, the chemical pulping process produces a pulp having fibers with a longer length than the fibers produced by the other pulping processes, particularly the mechanical pulping process. Accordingly, the industry has sought chemically produced pulp for use in disposable pads since the long fibers enhance the structural integrity and loft of the pad.
In spite that the chemical pulp results in a pad with desirable characteristics, a number of disadvantages are inherent in the use of such pulp. First, the chemical pulping process is relatively inefficient in that the yield of pulp to the amount of wood used in pulping is in the range of 40 to 55% whereas the yield of the mechanical, thermomechanical, and semichemical pulping processes is as high as 90-95%. The disparity in yields between the processes is due to the removal of lignin, cellulose, and hemicellulose from the wood during digestion in the chemical procedure. Accordingly, chemically produced pulps are significantly higher in cost than mechanical, thermomechanical, and semichemical pulps, necessarily resulting in a more costly item to the consumer. Also, the vital raw materials are not used to the desired extent in chemical pulps, thus detracting from our natural resources.
Second, environmental considerations favor the use of pulps which are not produced by the chemical process. In the chemical sulfite process, it is relatively difficult to reclaim the cooking chemicals used during pulping. Hence, the manufacturer must dispose of the chemicals, and it is believed that more than one sulfite processing plant has been closed due to contamination of water by the chemicals, which the Environmental Protection Agency considers dangerous. Although it is less difficult to reclaim the chemicals used in chemical kraft pulping, this process is characterized by the emission of gases containing malodorous substances, such as mercaptans and organic sulfides, and is also repugnant to the community at large.
Third, the energy required to fiberize pulp board solely of the chemical type is greater than that necessary for a pulp board containing mechanical or thermomechanical produced pulp. This follows since lignin of the fibers is removed during chemical pulping, thus increasing hydrogen bonding between dry fibers of the chemical pulp.
Finally, it is preferred to obtain an absorbent pad which overcomes the above objections, and yet has superior properties when used in the article. For example, the fibers in pads made solely from chemical pulps are relatively hydrophilic, and collapse when wetted and placed under loads, thus reducing the interfiber spacings in the pad. Thus, although readily absorbent, the fluid holding capacity of the pad becomes reduced where wetted and compressed, and the pad tends to cause backwetting through the cover sheet in this area.